Another sample of the rock material found on the Big Obsidian Flow trail. This sample not only illustrates the multiple flows that occured during the Big Obsidian eruption but the effects of varying gas content and cooling has on the lava. Notice the white rock (light-weight pumice ash), the black rock in the center (low grade obsidian), and the porous gray stone (frothy obsidian) just below the black rock. All are technically rhyolite but have different gas content and varying cooling history.